Wastes may be hazardous because of their chemical properties, their nuclear properties, or both. When the hazardous nature possible to convert the chemicals into innocuous substances by, for example, burning or reacting with other chemicals. However, many hazardous chemicals are substantially inert to other chemicals, and serious ojections have been raised to burning wastes, even when the burning is to be carried out at sea.
Radioactive wastes present a more difficult problem than do chemical wastes. An element's radioactivity is reduced only by the passage of time, and many radioactive elements have half-lives long enough to require their isolation for many human generations. Radioactive wastes have been characterized as high-level wastes (HLW), as for example depleted nuclear reactor fuels, and low-level-wastes (LLW), as for example, contaminated laboratory trash, and defueled nuclear submarines.
High level wastes, as defined by the International Atomic Energy Agency (IAEA), are those wastes which contain at least one Curie (3.7.times.10.sup.10 disintegrations per second) per metric ton of alpha emitters, or 100 Curies per metric ton of beta and/or gamma emitters. If the radioactive material is tritium the activity must be at least 10.sup.6 Curies per ton for the material to be considered HLW.
Low level wastes are any radioactive wastes which are not HLW, transuranic waste, mill tailings or any other material which may require shielding during transport or handling.
In view of the long term hazards of radioactive wastes, it has been a goal to isolate them as permanently as possible. Proposals have even been made to remove them permanently by sending them into space by rockets. However, the possibility of an atmosphere-polluting accident when rocketing these poisons into the sun or beyond our solar system mandates an earth-bound repository. However, the criteria for a permanent disposal site are severe. It must: be below any possible ground water level; be isolated from any form of plant, terrestrial, or aquatic life; be fixed in a place of minimum geo-dynamic activity, as for example volcanoes or earthquakes; have a minimum possibility of dispersion, advection, unauthorized disturbance by humans, or activities such as mining and wars, etc.; be susceptible to retrieval of the waste after a few decades, if necessary; and be suitable for monitoring as required.
The problem of disposing of radioactive wastes is accentuated by the large quantities of wastes which have been and are being produced. In 1982 the U.S.A. had about 312,000 m.sup.3 of HLW, over 99% of which were from the military and the rest from civilian sources. About 205,000,000 gallons of HLW byproduct from U.S. production of plutonium for the military was stored in tanks at Idaho Falls, Id.; Savannah River, Aiken, South Carolina; and Hanford Reservation, Richland, Washington in 1974, at which time it was understood that the rate of increase of stored material was 7,500,000 gallons per year. The thirty metric tons of spent fuel rods produced each year by a typical reactor have typically been stored "temporarily" near the commercial electric generating plants which used them.
In general, the heat-generation capabilities of HLW range from about 7.7-200 watts/m.sup.3 and average about 13.4 watts/m.sup.3. The afore-mentioned 312,000 m.sup.3 (approximately equal to 1,500,000 fifty-five gallon drums) generates over 4 Megawatts. The world's accumulation of spent fuel was about 44,500 metric tons of uranium in 1980, of which about 6600 metric tons was accumulated in the U.S.A. In 1985, the corresponding amounts were estimated to be about 82,000 and about 14,000 metric tons. It is estimated that the quantities in 1990 will be 145,000 metric tons worldwide and about 27,000 metric tons for the United States, and for the year 2000 the estimated quantities are 257,000 and 58,000 metric tons respectively.
Between 1946 and 1970 the United States had dumped over 90,000 fifty-five gallon steel drums of concrete-encapsulated LLW in both U.S. oceans at locations ranging from 15 to 220 miles offshore. Also, according to U.S. News and World Report, quoted by Park et al, "Disposal of Radioactive Wastes in the Ocean", Sea Technology, January 1984, pp. 62, 64, the United States at that time had approximately 8000 tons of HLW in temporary underwater storage.
In a special report to the President and the Congress entitled "Nuclear Waste Management and the Use of the Sea" (April 1984), the National Advisory Committee on Oceans and Atmosphere (NACOA) referenced many reports from the Department of Energy (DOE), the Environmental Protection Agency (EPA), the U.S. Nuclear Regulatory Commission (NUREG); the Office of Technical Assessment; The Ford Foundation; the International Atomic Energy Agency (IAEA); the General Accounting Office; congressional sub-committees; the National Academy of Sciences; the Union of Concerned Scientists; foreign government reports; individual technical publications as, for example, Science, and Health Physics; and individual authors (under Dewey Decimal System classification system numbers TD898 . . . ), concerning the problem of safeguarding terrestrial, aquatic, and atmospheric life. As these and other publications make clear, because hazardous radioactive waste has a lethal potency ranging from decades to multiples of 10.sup.5 years depending on the half-life and concentration, it must be kept from contaminating waters, soils, and atmosphere during this period of danger.
Nevertheless, in view of the many formidable technical and political obstacles which apply to other modes of waste disposal, there has been a continuing and active interest in proposals for deep water subseabed storage. Despite this active interest, and the expenditure of many millions of dollars on research, there is a dearth of truly practical and dependable methods for subseabed disposal in deep water environments.
Two categories of proposals for subseabed burial techniques have received considerable attention in the belief that they could be useful for disposal of waste originating in the U.S. They include (a) the use of holes of various diameters which have been drilled to various depths, and (b) the use of free-falling or propelled torpedo-shaped projectiles.
Drilled hole techniques include the introduction of waterdiluted, liquidized HLW into porous geologic formations in a manner similar to petroleum recovery, using similar technology. Also, it has been proposed to deposit small containers of encapsulated waste into pre-drilled bore-holes or "wells".
Injection of fluid waste into porous strata under the very deep waters (e.g. 5000 feet or more) which are of particular interest for subseabed burial would involve highly complex technology as well as major hazards in the transfer of the waste from a surface vessel to the deep-water bore-hole. Introduction of containerized waste into bore holes especially in the sands or visco-elastic muds which are often found under these deep waters could be frustrated by cave-ins and has not therefore achieved wide-spread acceptance.
The above-mentioned projectiles are used in self-burial methods and necessarily have a very limited capacity in order to be able to penetrate a desired minimum distance of about 30 meters into the seabed. This projectile method involves depth-of-burial measuring instrumentation with wireless transmission of this data back to the surface. Recovery of projectiles for monitoring or correction of insufficient penetration is difficult in view of the wide area in which they would be dispersed, e.g., about 100 meters apart.
A projectile method tested by Sandia National Laboratories employed a free-falling or propelled container (hydrodynamically streamlined) of cigar or torpedo shape about 1 foot in diameter and 16 feet long with a total storage volume of about two barrels or less. The burial force-time characteristic is an impulse generated by the change in momentum of the projectile, and the burial depth is dependent upon its kinetic energy and the soil resistance since no extra driving energy is applied after this projectile touches or reaches the bottom.
Given the problems of control over position and depth of burial and limited capacity for handling large volumes of waste which apply to the projectile method, the potential for cave-ins in the container-in-bore-hole method and the hazards and complexity which would be involved if liquid injection techniques were applied in deep water environments, the efforts expended on them show that development of a truly suitable method is currently beyond the level of ordinary skill in the art. In this connection, a widely recognized and respected researcher of ocean burial methods for waste has predicted that the technology to bury wastes in the ocean floor will not be ready until the first part of the 21st century; G. R. Heath, Sea Technology, Compass Publications, Arlington, Va., October 1984, pp. 71-72.